1. Field of the Invention
The present invention relates to a volume control apparatus and a volume control program, and more particularly, to a volume control apparatus and a volume control program that control volume by adjusting the level of an audio signal.
2. Description of the Related Art
On audio apparatuses such as CD players, DVD players, HDD players, and AV amplifiers, a volume control apparatus that controls volume to be outputted to the outside is mounted. Recently, a number of volume control apparatuses using a rotary encoder have appeared. Such volume control apparatuses control an internal electronic volume based on a pulse train outputted from the rotary encoder. Conventional volume control apparatuses are set such that regardless of the volume level the volume level changes depending only on the rotation angle of the rotary encoder, and thus have a problem of poor operability.
A technique for solving such a problem is disclosed in Japanese Patent Application Laid Open No. 2001-28525. A volume control apparatus disclosed in this document determines an amount of change in volume level based on the operating speed of a rotary encoder and a current volume level. Specifically, in the case of increasing the volume level, the lower the current volume level the amount of change in volume level relative to the operating speed of the rotary encoder is made larger, and the higher the current volume level the amount of change in volume level relative to the operating speed is made smaller. Therefore, with respect to the same operating speed, when the volume level is low the amount of change can be made large, and when the volume level is high the amount of change can be made small. As a result, the operability improves.
Meanwhile, recently, a volume control apparatus in which a digital signal processor (hereinafter, referred to as the DSP) is provided at the previous stage of an electronic volume has appeared. The DSP can control the amplitude and frequency characteristic of an audio signal and thus can control sound quality to a desired one.
When the amplitude and the frequency characteristic are corrected by the DSP, if the level of a corrected audio signal exceeds 0 dB, then a so-called overflow may occur. To prevent occurrence of such an overflow, normally, the DSP performs a scaling process in which the level of a received audio signal is attenuated in advance by a predetermined amount.
In the case of adopting the technique described in Japanese Patent Application Laid Open No. 2001-28525 to a volume control apparatus in which a DSP that performs such a scaling process is provided at the previous stage of an electronic volume, noise or an unusual sound may be generated. Since an audio signal attenuated in advance by a scaling process by the DSP is inputted to the electronic volume, even when the level of an audio signal to be outputted to the outside is less than 0 dB, the electronic volume may perform an amplification process instead of an attenuation process. In this case, an amount of change determined based on a current volume level and an operating speed is too large and thus noise or an unusual sound may be generated.